Stabilization of body balance with Light Touch following a mechanical perturbation: Adaption of sway and disruption of right posterior parietal cortex by cTBS

Abstract

Light touch with an earth-fixed reference point improves balance during quite standing. In our current study, we implemented a paradigm to assess the effects of disrupting the right posterior parietal cortex on dynamic stabilization of body sway with and without Light Touch after a graded, unpredictable mechanical perturbation. We hypothesized that the benefit of Light Touch would be amplified in the more dynamic context of an external perturbation, reducing body sway and muscle activations before, at and after a perturbation. Furthermore, we expected sway stabilization would be impaired following disruption of the right Posterior Parietal Cortex as a result of increased postural stiffness. Thirteen young adults stood blindfolded in Tandem-Romberg stance on a force plate and were required either to keep light fingertip contact to an earth-fixed reference point or to stand without fingertip contact. During every trial, a robotic arm pushed a participant's right shoulder in medio-lateral direction. The testing consisted of 4 blocks before TMS stimulation and 8 blocks after, which alternated between Light Touch and No Touch conditions. In summary, we found a strong effect of Light Touch, which resulted in improved stability following a perturbation. Light Touch decreased the immediate sway response, steady state sway following re-stabilization, as well as muscle activity of the Tibialis Anterior. Furthermore, we saw gradual decrease of muscle activity over time, which indicates an adaptive process following exposure to repetitive trials of perturbations. We were not able to confirm our hypothesis that disruption of the rPPC leads to increased postural stiffness. However, after disruption of the rPPC, muscle activity of the Tibialis Anterior is decreased more compared to sham. We conclude that rPPC disruption enhanced the intra-session adaptation to the disturbing effects of the perturbation.

Balance Adaptation While Standing on a Compliant Base Depends on the Current Sensory Condition in Healthy Young Adults

“…We had postulated that a process of postural adaptation would take place, also in the absence of reactions to external artificial stimulation(s), and reflect a progressive involvement of higher centres (Mierau et al, 2015;Kaulmann et al, 2020). We leveraged the use of the modulations in the frequency of the power spectrum of the CoP excursions (Schumann et al, 1995), following the approach exploited in several studies on balance adaptation to postural disturbance (Loughlin et al, 1996; Kiers et al, 2015;Borel and Ribot-Ciscar, 2016;Assländer et al, 2020).…”

“…During postural perturbations and during walking, body stability is enhanced by light touch to a fixed frame (Dickstein and Laufer, 2004;Forero and Misiaszek, 2013;Martinelli et al, 2015;Kaulmann et al, 2020). Light touch rapidly reaches the somatosensory cortex (Schieppati and Ducati, 1984) and deactivation of the sensory cortex is related to worse balance performance in old age (Noohi et al, 2019).…”

“…Haptic information, be it by tactile passive sensory inputs or light fingertip touch, has an effect comparable to vision (Holden et al, 1994;Rogers et al, 2001;Honeine and Schieppati, 2014;Chen et al, 2018) or to the vestibular system (Creath et al, 2008), even when standing on foam (Krishnan and Aruin, 2011;Albertsen et al, 2012). The continuous haptic input from the fingertip lightly touching an earth-fixed surface improves the control of upright stance under both stable or unstable stance (Clapp and Wing, 1999), after a perturbation (Johannsen et al, 2007) and during walking (Dickstein and Laufer, 2004;Forero and Misiaszek, 2013;Martinelli et al, 2015;Kaulmann et al, 2020) and in patients with poor balance (see Horak, 2009;Baldan et al, 2014). Hence, vision, proprioception, and haptic feedback have substantial effects in helping the body cope with perturbations of upright stance.…”

Specific Posture-Stabilising Effects of Vision and Touch Are Revealed by Distinct Changes of Body Oscillation Frequencies

“…It can selectively originate from touch receptors (64) and occurs with contact forces below those necessary to mechanically stabilise the body (65)(66)(67). Touch-induced stabilisation occurs both when standing on firm ground and when standing on foam (68,69) or after a balance perturbation (70,71). With eyes closed, a light touch of an object next to the body, or a touch of the ground by the cane (66,72), modifies the control of posture, because finger or cane can be appropriately moved to get the information they are searching for (73).…”

Keeping in step with the young: Chronometric and kinematic data show intact procedural locomotor sequence learning in older adults

“…The detection of regularities in environmental dynamics allows the preparation of postural adjustments to minimize the impact of any balance disturbance. This learning to predict the sequence of environmental stimuli is important to prevent an unintended destabilization of balance and a fall [ 16 ]. The complexity of postural and locomotor responses stems from the planning of sequences of several postural adjustments to ensure postural stability before any voluntary response can be executed.…”